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The life cycle of a dioicous bryophyte. The gametophyte (haploid) structures are shown in green, the sporophyte (diploid) in brown. Like all land plants (embryophytes), bryophytes have life cycles with alternation of generations. [11]
By contrast, mosses and other bryophytes have only a single set of chromosomes and so are haploid (i.e. each chromosome exists in a unique copy within the cell). There is a period in the moss life cycle when they do have a double set of paired chromosomes, but this happens only during the sporophyte stage.
Diagram showing the alternation of generations between a diploid sporophyte (bottom) and a haploid gametophyte (top) Alternation of generations (also known as metagenesis or heterogenesis) [1] is the predominant type of life cycle in plants and algae.
The gametophyte is the first and dominant phase of two alternating phases in a bryophyte's life cycle. This part of the life cycle consists of protonema (the preliminary stage where the propagule develops green thread-like filaments), the rhizoids (filaments growing beneath the bryophyte that help anchor the bryophyte to its substratum), the stem, the leaves, its reproductive structure ...
In all bryophytes, the primary plants are the haploid gametophytes, with the only diploid portion being the attached sporophyte, consisting of a stalk and sporangium. Because these plants lack lignified water-conducting tissues, they cannot become as tall as most vascular plants. Algae, especially green algae. The algae consist of several ...
Genera such as Rhynia have a similar life-cycle but have simple tracheids and so are a kind of vascular plant. [44] It was assumed that the gametophyte dominant phase seen in bryophytes used to be the ancestral condition in terrestrial plants, and that the sporophyte dominant stage in vascular plants was a derived trait.
As in mosses and liverworts, hornworts have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information; the flattened, green plant body of a hornwort is the gametophyte stage of the plant. Hornworts may be found worldwide, though they tend to grow only in places that are damp or humid.
A protonema (plural: protonemata) is a thread-like chain of cells that forms the earliest stage of development of the gametophyte (the haploid phase) in the life cycle of mosses. When a moss first grows from a spore , it starts as a germ tube , which lengthens and branches into a filamentous complex known as a protonema , from which a leafy ...